* {
    margin: 0;
    padding: 0;
}

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    /* 渐变背景 */
    background: linear-gradient(200deg, #00c6fb, #66a6ff);
}

nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
    li {
        $c: #fff;
        color: $c;
        width: 240px;
        height: 60px;
        border: 3px solid $c;
        border-radius: 10px;
        text-align: center;
        line-height: 60px;
        font-weight: bold;
        cursor: pointer;
        margin: 30px;
        position: relative;
        overflow: hidden;
        z-index: 1;
        transition: 0.5s;
        &:hover {
            color: #222;
            span {
                transform: translateY(0) scale(2);
            }
        }
        span {
            position: absolute;
            width: 25%;
            height: 100%;
            background-color: $c;
            border-radius: 50%;
            transform: translateY(150%);
            transition: 0.5s;
            z-index: -1;
            @for $i from 1 to 5 {
                &:nth-child(#{$i}) {
                    left: calc(($i - 1) * 25%);
                    transition-delay: calc(($i - 1) * 0.1s);
                }
            }
        }
    }
}
